Oilseeds typically contain from about 20 percent oil to about 50 percent oil by weight, with the percentages varying with the type of oilseed. Generally, the seed is pressed, with or without a prior heat treatment step, to obtain a pressed oil and a pressed seedcake. Generally, the pressed seedcake is then solvent extracted to remove or reduce the remaining oil. Removing the residual solvent from the meal is generally performed by heating the meal to evaporate the residual solvent, and in the process, the meal is toasted. As a result of the heating/toasting of the meal, a significant portion of the protein is denatured, rendering much of the protein less soluble in many solvents. After removal of the solvent from the pressed seedcake and drying of the seedcake, there generally remains a toasted, toasted defatted meal, which contains from about 25% to about 55% of protein on a dry weight basis.
Some toasted defatted meals, depending upon the oilseed, contain a high amount of fiber, as well as other anti-nutritional factors and undesirable compounds, such as glucosinolates, phytic acid or phytates, sinapine and sinigrin. The fiber and anti-nutritional factors present in the protein render the toasted defatted meal unattractive for commercial uses. In addition, toasted meal is not generally used as a source of protein, because of its high percentage of insoluble protein, which is difficult to remove from the fiber.
In the case of toasted canola defatted meal, one method of separating the protein from the fiber, anti-nutritional factors and other undesirable compounds has been to dissolve the canola protein in a high ionic strength (i.e. high salt content) aqueous solution. This results in the canola protein dissolving in the aqueous solution, while the fiber is insoluble. However, the salt is difficult and uneconomical to remove and recover from the resultant canola protein solution.